“The Vaccine Revolt, or Revolta da Vacina, was a popular revolt that occurred in Rio between November 10th and 16th, 1904. A lot of violent, urban conflicts took place during those days among the poor and the authorities.
The main cause was the compulsory vaccination campaign against smallpox, conducted by the Brazilian government, led by public health physician Dr. Oswaldo Cruz (who had just created the Mandatory Vaccination Law, whose passing by Congress was the spark that set off the revolts). The vast majority of the population, made up of poor and uninformed people were not aware of the way vaccines work and, therefore, did not want to take it.
The other cause was the climate of popular discontent with other measures taken by the federal government, which mainly affected the poorest people. Among these measures, we can highlight the urban renewal of the city of Rio de Janeiro (popularly called the “bota abaixo“), which displaced thousands of people so that tenement and public housing could be destroyed (see below) to make way for the construction of boulevards, gardens and more modern buildings.
During the event, a lot of people didn’t want to receive the health practicioners in their homes and reacted violently towards the idea they could be forced to take a vaccine. The people revolted by attacking and damanging many public properties such as buildings and stores. Also, they removed parts of the trolley tracks and overturned the trolleys themselves.
The government reacted by temporarily suspending the mandatory vaccination program, suspended people’s rights and brought in the army to deal with them. After 30 deaths and 100 injuries, the military had things under control and the program was reinstated. – Source (PT)
One additional but important detail that wasn’t mentioned above is that “Dr. Cruz created the Brigadas Mata Mosquitos (Mosquito-Killing Brigades, above), groups of sanitary service workers who entered homes in order to exterminate the mosquitoes which transmitted yellow fever. The campaign also worked to exterminate rats which transmitted bubonic plague, distributing rat poison and requiring proper handling, storage, and collection of garbage.” Source